<!-- Getting Started -->

<h2 id="introduction">Introduction</h2>

<p>Go is an open source project, distributed under a
<a href="/LICENSE">BSD-style license</a>.
This document explains how to check out the sources,
build them on your own machine, and run them.
</p>

<div class="detail">

<p>
There are two distinct ways to experiment with Go.
This document focuses on the <code>gc</code> Go
compiler and tools (<code>6g</code>, <code>8g</code> etc.).
For information on how to use <code>gccgo</code>, a more traditional
compiler using the GCC back end, see
<a href="gccgo_install.html">Setting up and using gccgo</a>.
</p>

<p>
The Go compilers support three instruction sets.
There are important differences in the quality of the compilers for the different
architectures.
</p>

<dl>
<dt>
	<code>amd64</code> (a.k.a. <code>x86-64</code>); <code>6g,6l,6c,6a</code>
</dt>
<dd>
	The most mature implementation.  The compiler has an effective optimizer
	(registerizer) and generates good code (although <code>gccgo</code>
	can do noticeably better sometimes).
</dd>
<dt>
	<code>386</code> (a.k.a. <code>x86</code> or <code>x86-32</code>); <code>8g,8l,8c,8a</code>
</dt>
<dd>
	Comparable to the <code>amd64</code> port.
</dd>
<dt>
	<code>arm</code> (a.k.a. <code>ARM</code>); <code>5g,5l,5c,5a</code>
</dt>
<dd>
	Incomplete.
	It only supports Linux binaries, the optimizer is incomplete,
	and floating point uses the VFP unit.
	However, all tests pass.
	Work on the optimizer is continuing.
	Tested against a Nexus One.
</dd>
</dl>

<p>
Except for things like low-level operating system interface code, the run-time
support is the same in all ports and includes a mark-and-sweep garbage collector
(a fancier one is in the works), efficient array and string slicing,
support for segmented stacks, and a strong goroutine implementation.
</p>

<p>
The compilers can target the FreeBSD, Linux,
and OS X (a.k.a. Darwin) operating systems.
(A port to Microsoft Windows is in progress but incomplete.  See the 
<a href="http://code.google.com/p/go/wiki/WindowsPort">Windows Port</a>
page for details.)
The full set of supported combinations is listed in the discussion of
<a href="#environment">environment variables</a> below.
</p>

</div>

<h2 id="ctools">Install C tools, if needed</h2>

<p>The Go tool chain is written in C.
To build it, you need these programs installed: 
<ul>
<li>GCC, 
<li>the standard C libraries, 
<li>the parser generator Bison,
<li>GNU <tt>make</tt> (version 3.81 or later),
<li><tt>awk</tt>, and 
<li>the text editor <tt>ed</tt>.
</ul>
</p>

<p>On OS X, they can be
installed as part of
<a href="http://developer.apple.com/TOOLS/Xcode/">Xcode</a>. 
</p>

<p>On Ubuntu/Debian, use <code>sudo apt-get install bison ed gawk gcc libc6-dev
make</code>. If you want to build 32-bit binaries on a 64-bit system you'll
also need the <code>libc6-dev-i386</code> package.
</p>

<h2 id="mercurial">Install Mercurial, if needed</h2>

<p>
To perform the next step you must have Mercurial installed. (Check that you  have an <code>hg</code> command.) This suffices to install Mercurial on most systems:
</p>
<pre>
sudo easy_install mercurial
</pre>
(On Ubuntu/Debian, you might try <code>apt-get install python-setuptools
python-dev build-essential</code> first. The Mercurial in your distribution's
package repository will most likely be old and broken.)
</p>
<p>
If that fails, try installing manually from the <a href="http://mercurial.selenic.com/wiki/Download">Mercurial Download</a> page.</p>
</p>

<p>
Mercurial versions 1.7.x and up require the configuration of
<a href="http://mercurial.selenic.com/wiki/CACertificates">Certification Authorities</a>
(CAs). Error messages of the form:
</p>
<pre>
warning: go.googlecode.com certificate with fingerprint b1:af: ... bc not verified (check hostfingerprints or web.cacerts config setting)
</pre>
<p>
when using Mercurial indicate that the CAs are missing.
Check your Mercurial version (<code>hg --version</code>) and
<a href="http://mercurial.selenic.com/wiki/CACertificates#Configuration_of_HTTPS_certificate_authorities">configure the CAs</a>
if necessary.
</p>

<h2 id="fetch">Fetch the repository</h2>

<p>
<p>Go will install to a directory named <code>go</code>.
Change to the directory that will be its parent
and make sure the <code>go</code> directory does not exist.
Then check out the repository:</p>

<pre>
$ hg clone -u release https://go.googlecode.com/hg/ go
</pre>

<h2 id="install">Install Go</h2>

<p>
To build the Go distribution, run
</p>

<pre>
$ cd go/src
$ ./all.bash
</pre>

<p>
If all goes well, it will finish by printing output like:
</p>

<pre>
ALL TESTS PASSED

---
Installed Go for linux/amd64 in /home/you/go.
Installed commands in /home/you/go/bin.
*** You need to add /home/you/go/bin to your $PATH. ***
The compiler is 6g.
</pre>

<p>
where the details on the last few lines reflect the operating system,
architecture, and root directory used during the install.
</p>

<div class="detail">

<p>For more information about ways to control the build,
see the discussion of <a href="#environment">environment variables</a> below.</p>
</div>

<h2 id="writing">Writing programs</h2>

<p>
Given a file <code>file.go</code>, compile it using
</p>

<pre>
$ 6g file.go
</pre>

<p>
<code>6g</code> is the Go compiler for <code>amd64</code>; it will write the output
in <code>file.6</code>. The &lsquo;<code>6</code>&rsquo; identifies
files for the <code>amd64</code> architecture.
The identifier letters for <code>386</code> and <code>arm</code>
are &lsquo;<code>8</code>&rsquo; and &lsquo;<code>5</code>&rsquo;.
That is, if you were compiling for <code>386</code>, you would use
<code>8g</code> and the output would be named <code>file.8</code>.
</p>

<p>
To link the file, use
</p>

<pre>
$ 6l file.6
</pre>

<p>
and to run it
</p>

<pre>
$ ./6.out
</pre>

<p>A complete example:
</p>

<pre>
$ cat &gt;hello.go &lt;&lt;EOF
package main

import "fmt"

func main() {
	fmt.Printf("hello, world\n")
}
EOF
$ 6g hello.go
$ 6l hello.6
$ ./6.out
hello, world
$
</pre>

<p>
There is no need to list <code>hello.6</code>'s package dependencies
(in this case, package <code>fmt</code>) on the <code>6l</code>
command line.
The linker learns about them by reading <code>hello.6</code>.
</p>

<div class="detail">
<p>
To build more complicated programs, you will probably
want to use a
<code>Makefile</code>.
There are examples in places like
<code>go/src/cmd/godoc/Makefile</code>
and <code>go/src/pkg/*/Makefile</code>.
The
<a href="contribute.html">document</a>
about contributing to the Go project
gives more detail about
the process of building and testing Go programs.
</p>
</div>

<h2 id="next">What's next</h2>

<p>
Start by reading the <a href="go_tutorial.html">Go Tutorial</a>.
</p>

<p>
Build a web application by following the <a href="codelab/wiki/">Wiki
Codelab</a>.
</p>

<p>
Read <a href="effective_go.html">Effective Go</a> to learn about writing
idiomatic Go code.
</p>

<p>
For the full story, consult Go's extensive 
<a href="docs.html">documentation</a>.
</p>

<h2 id="releases">Keeping up with releases</h2>

<p>
The Go project maintains two stable tags in its Mercurial repository:
<code>release</code> and <code>weekly</code>.
The <code>weekly</code> tag is updated about once a week, and should be used by
those who want to track the project's development.
The <code>release</code> tag is given, less often, to those weekly releases
that have proven themselves to be robust.
</p>

<p>
Most Go users will want to keep their Go installation at the latest
<code>release</code> tag.
New releases are announced on the
<a href="http://groups.google.com/group/golang-announce">golang-announce</a>
mailing list.
</p>

<p>
To update an existing tree to the latest release, you can run:
</p>

<pre>
$ cd go/src
$ hg pull
$ hg update release
$ ./all.bash
</pre>

<p>
To use the <code>weekly</code> tag run <code>hg update weekly</code> instead.
</p>

<h2 id="community">Community resources</h2>

<p>
For real-time help, there may be users or developers on
<code>#go-nuts</code> on the <a href="http://freenode.net/">Freenode</a> IRC server.
</p>

<p>
The official mailing list for discussion of the Go language is
<a href="http://groups.google.com/group/golang-nuts">Go Nuts</a>.
</p>

<p>
Bugs can be reported using the <a href="http://code.google.com/p/go/issues/list">Go issue tracker</a>.
</p>

<p>
For those who wish to keep up with development,
there is another mailing list, <a href="http://groups.google.com/group/golang-checkins">golang-checkins</a>,
that receives a message summarizing each checkin to the Go repository.
</p>

<h2 id="environment">Environment variables</h2>

<p>
The Go compilation environment can be customized by environment variables.
None are required by the build, but you may wish to set them
to override the defaults.
</p>

<dl>
<dt>
	<code>$GOROOT</code>
</dt>
<dd>
	The root of the Go tree, often <code>$HOME/go</code>.
	This defaults to the parent of the directory where <code>all.bash</code> is run.
	If you choose not to set <code>$GOROOT</code>, you must
	run <code>gomake</code> instead of <code>make</code> or <code>gmake</code>
	when developing Go programs using the conventional makefiles.
</dd>

<dt>
	<code>$GOROOT_FINAL</code>
</dt>
<dd>
	The value assumed by installed binaries and scripts when
	<code>$GOROOT</code> is not set.
	It defaults to the value used for <code>$GOROOT</code>.
	If you want to build the Go tree in one location
	but move it elsewhere after the build, set 
	<code>$GOROOT_FINAL</code> to the eventual location.
</dd>

<dt>
<code>$GOOS</code> and <code>$GOARCH</code>
</dt>
<dd>
	The name of the target operating system and compilation architecture.
	These default to the values of <code>$GOHOSTOS</code> and
	<code>$GOHOSTARCH</code> respectively (described below).

	<p>
	Choices for <code>$GOOS</code> are <code>linux</code>,
	<code>freebsd</code>,
	<code>darwin</code> (Mac OS X 10.5 or 10.6),
	and <code>windows</code> (Windows, an incomplete port).
	Choices for <code>$GOARCH</code> are <code>amd64</code> (64-bit x86, the most mature port),
	<code>386</code> (32-bit x86), and
	<code>arm</code> (32-bit ARM, an incomplete port).
	The valid combinations of <code>$GOOS</code> and <code>$GOARCH</code> are:
	<table cellpadding="0">
	<tr>
	<th width="50"><th align="left" width="100"><code>$GOOS</code></th> <th align="left" width="100"><code>$GOARCH</code></th> <th align="left"></th>
	</tr>
	<tr>
	<td></td><td><code>darwin</code></td> <td><code>386</code></td>
	</tr>
	<tr>
	<td></td><td><code>darwin</code></td> <td><code>amd64</code></td>
	</tr>
	<tr>
	<td></td><td><code>freebsd</code></td> <td><code>386</code></td>
	</tr>
	<tr>
	<td></td><td><code>freebsd</code></td> <td><code>amd64</code></td>
	</tr>
	<tr>
	<td></td><td><code>linux</code></td> <td><code>386</code></td>
	</tr>
	<tr>
	<td></td><td><code>linux</code></td> <td><code>amd64</code></td>
	</tr>
	<tr>
	<td></td><td><code>linux</code></td> <td><code>arm</code></td> <td><i>incomplete</i></td>
	</tr>
	<tr>
	<td></td><td><code>windows</code></td> <td><code>386</code></td> <td><i>incomplete</i></td>
	</tr>
	</table>
</dd>

<dt>
<code>$GOHOSTOS</code> and <code>$GOHOSTARCH</code>
</dt>
<dd>
	The name of the host operating system and compilation architecture.
	These default to the local system's operating system and
	architecture.

	<p>
	Valid choices are the same as for <code>$GOOS</code> and
	<code>$GOARCH</code>, listed above.
	The specified values must be compatible with the local system.
	For example, you should not set <code>$GOHOSTARCH</code> to 
	<code>arm</code> on an x86 system.
</dd>

<dt>
<code>$GOBIN</code>
</dt>
<dd>
	The location where binaries will be installed.
	The default is <code>$GOROOT/bin</code>.
	After installing, you will want to arrange to add this
	directory to your <code>$PATH</code>, so you can use the tools.
</dd>

<dt>
<code>$GOARM</code> (arm, default=6)
</dt>
<dd>
	The ARM architecture version the run-time libraries should target.
	ARMv6 cores have more efficient synchronization primitives. Setting
	<code>$GOARM</code> to 5 will compile the run-time libraries using
	just SWP instructions that work on older architectures as well.
	Running v6 code on an older core will cause an illegal instruction trap.
</dd>
</dl>

<p>
Note that <code>$GOARCH</code> and <code>$GOOS</code> identify the
<em>target</em> environment, not the environment you are running on.
In effect, you are always cross-compiling.
By architecture, we mean the kind of binaries
that the target environment can run:
an x86-64 system running a 32-bit-only operating system
must set <code>GOARCH</code> to <code>386</code>,
not <code>amd64</code>.
</p>

<p>
If you choose to override the defaults,
set these variables in your shell profile (<code>$HOME/.bashrc</code>,
<code>$HOME/.profile</code>, or equivalent). The settings might look 
something like this:
</p>

<pre>
export GOROOT=$HOME/go
export GOARCH=386
export GOOS=linux
</pre>
